Presently, contact lenses are constructed of certain types of plastic materials. For instance, commercial hard or essentially semirigid contact lenses are predominantly made from polymethylmethacrylate. However, this material is not completely satisfactory because of its poor gas permeation characteristics. This, in turn, induces edema on the surface of the cornea in the region covered by the contact lens and thereby resulting in complications and poor vision.
In order to overcome this problem of insufficient gas permeability, it has been suggested to provide contact lenses from various polymerizable silicone esters. These suggested contact lenses also include methyl methacrylate and/or certain other volatile esters of methacrylic acid and/or of acrylic acid.
Usually, rods of material from which these types of contact lenses can be lathed are prepared in capped tubes to prevent the loss of the volatile monomers during polymerization. Furthermore, these mixtures are polymerized over long periods of time in stages from low to more elevated temperatures to prevent the loss of the more volatile monomers. A problem with this method of material preparation has been that the material is not homogeneous throughout the length of the rod. Furthermore, undesirable side products can result from long polymerization times.
U.S. Pat. Nos. 3,808,178 and 4,120,570 to Gaylord suggest contact lenses fabricated from a copolymer of a polysiloxanylalkyl acrylic ester and an alkyl acrylic ester or alkyl methacrylate ester. It is reported that the copolymer has increased oxygen permeability. Wettability can be imparted to the copolymer by the addition of about 0.1 to about 10% by weight of one or more hydrophilic monomers such as hydroxyalkyl acrylates and methacrylates, acrylic and methacrylic acid, acrylamide, glycidyl acrylate and N-vinyl pyrrolidione.
The polysiloxanylalkyl acrylic esters suggested by Gaylord include those required by the present invention.
U.S. Pat. Nos. 4,152,508 and 4,330,383 to Ellis, et al. suggest hard contact lenses reportedly having high permeability obtained from a copolymerizing siloxanylalkyl ester with an ester of acrylic or methacrylic acid. In addition, in order to obtain improved physical characteristics over the materials suggested by Gaylord in U.S. Pat. Nos. 3,808,178 and 4,120,570 it is necessary, according to Ellis, et al. to employ an itaconate ester in the copolymerization. Representatives of itaconate esters include phenyl itaconate, diphenyl itaconate, methyl phenyl itaconate, and dimethyl itaconate.
U.S. Pat. No. 4,355,147 to Deichert, et al. suggests hard contact lenses by copolymerizing in certain relative amounts, polysiloxane monomers which must be .alpha., .omega. terminally bonded through divalent hydrocarbon groups to an activated unsaturated group; certain polycyclic acrylates or methacrylates; and a member selected from the group consisting of hydroxyethylmethacrylate, hydroxyethylacrylate, hydroxypropylmethacrylate, hydroxypropylacrylate, and mixtures thereof. Although the polycyclic acrylates or methacrylates suggested by Deichert, et al. include those required by the present invention, the polyfunctional polysiloxanes required therein are entirely different from those required by the present invention.
U.S. Pat. No. 4,327,203 to Deichert, et al. suggests contact lenses from the copolymerization of monomeric polysiloxanes endcapped with unsaturated groups; cycloalkyl acrylate or methacrylate, and a tear film stabilizer such as hydroxyethylmethacrylate, hydroxypropylmethacrylate, hydroxyethylacrylate, and hydroxypropylacrylate.
U.S. Pat. Nos. 4,153,641; 4,189,546; 4,208,506; and 4,341,889 to Deichert, et al. suggest compositions suitable for fabricating contact lenses by polymerizing certain difunctional siloxane materials.
U.S. Pat. Nos. 4,254,248; 4,276,402; and 4,277,595 suggest soft hydrophilic contact lenses obtained by copolymerizing certain difunctional siloxane materials and various cyclic esters of acrylic or methacrylic acid.
U.S. Pat. Nos. 4,242,483 and 4,306,042 suggest contact lenses fabricated from copolymerizing certain siloxanyl alkyl esters.
U.S. Pat. No. 4,139,513 suggests soft contact lenses from copolymerizing certain siloxanes.
The following patents also suggest contact lenses containing a siloxane: U.S. Pat. Nos. 4,062,627, 4,343,927, 3,808,179, 4,246,389, 4,182,822, 4,235,985, 4,138,382, 4,139,548, 4,139,692, 3,916,033, 4,248,989, 4,303,772, 4,242,483, 4,216,303, 4,245,069.
U.S. Pat. Nos. 3,681,298; 3,940,353; and 3,716,524 suggest copolymers from isobornyl methacrylate.